Boris Johnson's sister joins rival party for UK vote: reports

Family allegiances have been swept aside as the sister of Foreign Minister Boris Johnson has joined a rival party ahead of Britain's national election, according to media reports on Thursday.

File image of Rachel Johnson and Boris Johnson from 2012 Source: Getty Images

Rachel Johnson, a prominent columnist, has signed up to the pro-European Liberal Democrats ahead of the June 8 vote.

The centre-left party holds just nine seats in British parliament but is hoping to make gains against the ruling Conservatives by opposing the government's Brexit strategy.

Boris was a key Brexiteer ahead of last year's referendum which saw Britain vote to end its 44-year membership of the European Union.

His sister Rachel had hoped to fight for a parliamentary seat for the Lib Dems, but party rules state candidates must be members for at least a year, Channel 4 News and other media reported.

UK Foreign Minister Boris Johnson (AAP) Source: AAP

The Mail on Sunday columnist on Thursday retweeted a post by her husband supporting the party: "it's been 25 years since my wife @Rachelsjohnson agreed on anything - but then Brexit. I joined t LibDems 6 weeks ago. Why haven't you?"

The Lib Dems are yet to comment on their new high-profile supporter.

Rachel and Boris's brother, Jo Johnson, is also a Conservative MP who serves as universities minister.

Following the shock referendum outcome last June, Rachel said her daughter cried while her son complained his friends were "fuming" on Facebook.

"They’re all saying Boris has stolen our futures," she wrote in The Mail on Sunday, quoting her son.

But despite her Remain persuasions, she did not blame her brother: "Now I have to try to persuade my family -- and my daughter says that she is 'in mourning' -- that this is not all Boris's fault."

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